Oxygen on the periodic table
Oxygen, atomic number 8, symbol ‘O’, and molecular formula O2 is the most abundant chemical element of the Group-16 or chalcogen family in the periodic table. It makes up to 47 percent of the earth’s crust in the form of liquid and solid oxides, oxoacids, and gas forms. The elemental oxygen atoms is an isotopic mixture of O-16, O-17, and O-18 isotopes that occur in the natural environment 21 percent by volume in air, 86 percent by weight of liquid water in oceans, essential for living organisms (plant and animal). O-17 and O-18 are prepared by fractional distillation or electrolysis of water molecule or thermal diffusion of oxygen gas. Elemental oxygen isotope (mass number = 18) uses as the tracer in chemical kinetics and mechanistic studies but O-17 (mass number = 17) used in NMR spectrum analysis.
In learning chemistry, the outermost quantum shell consists of the 2s2 2p3 electronic configuration. The interesting facts about oxygen alone in the Group-16 or chalcogen family, they do not possess d-orbital. Therefore, oxygen only shows valency 2 but due to the presence of vacant d-orbitals other elements like sulfur, selenium, tellurium, and polonium possess 2, 4. and 6 valances for chemical bonding purposes.
Properties of Oxygen Gas
Oxygen (meting point = -229 °C and boiling point = -183 °C) has very high ionization energy among the group 16 chemical elements with a very low metallic character, commonly known as a nonmetal. With the increasing atomic number in group-16, the resistance of the elements decreases. Oxygen and sulfur are an insulator, selenium and tellurium are semiconductors but polonium is a metal conductor of electrical energy. Due to the 2s2 2p4 outer electronic formula, the elemental oxygen generally shows, -2 oxidation number or state in a chemical compound.
The elements are two electrons short of the next noble gas configuration. Therefore, when bonding with these two electrons achieved by gaining two electrons by electropositive elements or by making two single covalent bonds or one double bond with other elements. Oxygen has very high electronegativity and electron affinity in favor of the formation of the crystalline solid compounds with alkali (lithium, sodium, potassium) and alkaline (beryllium, magnesium, calcium) earth metals.
Oxygen (molar mass = 16 gm/mol) is a colourless, odourless, tasteless gas that occurs in two allotropic forms like dioxygen (molecular weight = 32 gm/mol) and ozone gas (molecular weight = 48 gm/mol). The colorless, orderless oxygen gas molecule is paramagnetic in nature with two unpaired electrons, pale blue in liquid state but blue in the crystal lattice. Dioxygen is fairly soluble in water and highly soluble in organic solvents like acetone and benzene and forms weak charge-transfer complexes.
In the ground state, the highest occupied molecular diagram of the oxygen molecule shows that the two electrons (parallel spin) in two pi-antibonding orbitals. It is said to the triplet state. But the next higher state, one in which the electrons are spin paired in pi-antibonding molecular orbitals. These states termed singlet states. Normally a triplet to singlet transition forbidden. The gaseous oxygen molecule colorless but in liquid or solid form, a single photon collides with other molecules and excites both. Absorption of electromagnetic spectrum radiation in the red region to the green visible region gives observed blue color.
Isolation of Chemical Element
Oxygen element or gas molecule obtained industrially by fractional distillation of liquid air but in the laboratory, it may be prepared from different chemical compounds like hydrogen peroxide, potassium chlorate, potassium permanganate, etc. Oxygen is produced by the catalytic decomposition of hydrogen peroxide over the platinum catalyst in nickel foil.
Thermal decomposition of potassium chlorate or 2KClO3 → 2KCl + O2. The reaction occurs at 400° to 500 °C. If we use manganese dioxide as a chemical catalyst, the reaction occurs at 150 °C. But this process also produces 3 percent of ClO2. Thermal decomposition of pure potassium permanganate in a vacuum at specific heat gives a very pure O2-molecule. 2KMnO4 → K2MnO4 + MnO2 + O2.
Uses of Oxygen
Oxygen is the third chemical in order of use in the industry after sulfuric acid and nitrogen and nearly 100 million tonnes of beings consumed annually throughout the world. It is largely used in metallurgy like steel making in blast furnaces and Bessemer converters. It is also used in direct oxidation in many chemical processes.
The colorless, odorless, tasteless oxygen (O2) gas molecule uses for making synthesis gas in chemistry, oxidizing organic hydrocarbon like methane, ethane, ethylene acetylene, etc, the oxidizer for the fuels in rocket propulsion.
Uses of oxygen in the body
Oxygen is an essential chemical element of the animal or plant body. It is carried out by two metalloproteins like hemoglobin and myoglobin of our body. Besides hemoglobin and myoglobin, there are two other dioxygen transport proteins hemocyanins and hemerythrin. Hemerythrin found in marine invertebrates.
An adult human contains about 5-liter of blood. Each milliliter of blood contain 5000 million blood cells and each cell contains 0.25 million hemoglobin molecule. The red blood cells have a life span of 100 to 120 days. Therefore 1 percent of hemoglobin molecule replaced daily. While hemoglobin is essential for oxygen transport in our body. Myoglobin is engaged in the storage of oxygen in muscle tissues and used when necessary. The oxygen in our body is used in the biosynthesis of many compounds in the metabolic chain. It converts some lipid-soluble molecule to water-soluble that suitable for excretion.